Astell&Kern SP4000 DAP Review: Audio Perfection with Unlimited Potential
Read Time: Approx. 20 min.
TL;DR
- First Astell&Kern DAP with full Android OS and Google Play Store access: Download any app you want
- True Quad DAC Architecture with 131 dB SNR and advanced audio technologies
- Reference-level sound quality that's pure, articulate, and detailed for discerning audiophiles
The First Full Android Flagship That Redefines Portable Audio
Think of the top three audiophile-grade DAPs on the market today, and I can bet you at least two out of the three are manufactured by Astell&Kern. Even with numerous DAP manufacturers to choose from, Astell&Kern has cornered the market as the audiophile's #1 choice for portable audio players. From the KANN series to the flagship A&ultima line, Astell&Kern DAPs offer the very best in sound quality and performance.
It's been almost three years since Astell&Kern released its flagship player, the A&ultima SP3000 DAP. Following up on any flagship product is no easy feat, especially a product like the SP3000 DAP, which was regarded as the ultimate reference player. So when rumblings of a new flagship player started to emerge, every audiophile (including myself) was eager to see how AK planned to "one-up" the SP3000.
Announced at this year's High End Munich Show, the Astell&Kern A&ultima SP4000 Digital Audio Player is the company's first DAP to support the full Android OS. Long-time AK users surely understand the magnitude of an advancement like this. While the SP3000 inspired the SP4000 in many ways, it takes the crown as the ultimate reference player with Android OS support, circuit innovations, advanced DAR technology, and more.
PROS
- FULL ANDROID OS!! APPS GALORE
- Signature AK Sound Perfected: Detailed, articulate, dynamic
- Large screen, new UI features, included case
CONS
- Heavy. Will weigh down your pocket
- Extremely responsive screen= highly sensitive
Design
- 6" 2K Touch Screen, 21.7 oz
- Stainless Steel 904L Body
- 3.5mm, 4.4mm headphone jacks
- USB-C Port, Control Lock Switch, Volume/Power Wheel
- 256GB Internal Memory, 1.5TB MicroSD Slot
If there's one thing Astell&Kern has mastered as a company, it's clear brand recognition. Between the iconic volume wheel and sharp, beveled edges, anyone familiar with an AK DAP can instantly recognize it. The SP4000's design is supremely Astell&Kern.
At 21.7 oz with a stainless steel 904L body, the A&ultima SP4000 DAP is the heaviest player released by Astell&Kern to date. While it may be on the heavier side, 904L stainless steel provides excellent corrosion resistance, so the trade-off is worth it. It retains a lot of the SP3000's styling while still being unique in its own right. It's slightly larger than the SP3000, with a gradual taper going from the top of the DAP to the bottom. I have tiny hands, so I was afraid I wouldn't be able to hold it well one-handed, but the tapered design and beveled edge on the right side allow me to have a surprisingly secure grip.
While it sports a slightly different shape than the SP3000, the functionality in terms of buttons and physical controls remains roughly the same. The volume wheel on the right side doubles as the power button, illuminating different colors depending on the bit depth of the song currently playing. Astell&Kern has ditched the 2.5mm jack on the SP3000 and added a control lock switch to sit alongside the single-ended 3.5mm headphone jack and balanced 4.4mm jack on the top. Charging and data transfer (USB DAC mode) are done via the USB-C input on the bottom, where you'll also find the microSD slot supporting up to 1.5TBs of additional storage–that's on top of the 256GB of internal memory. The left side of the player houses the basic playback controls: skip, pause, and play.
The SP4000's 6-inch 2K screen is a welcome upgrade, delivering better resolution and detail than the 5.46" full HD screen on the SP3000. Screen size aside, the clarity and vibrant color of the screen are so impressive that I feel like I'm holding a top-of-the-line PC monitor in my hand. With a 6,780mAh 3.8V Li-Polymer battery boasting 10 hours of playback after 4 hours of charging (PD 3.0 Fast Charging), you'll have no problem using the SP4000 during your daily commute. Connectivity can be achieved through Dual-band Wi-Fi, DLNA networking, the USB-C port, and Bluetooth 5.0 with support for high-resolution codecs like LDAC and LHDC, among others. The SP4000 is a Roon Ready and Roon Tested device.
Included with the SP4000 is a premium Perlinger Shrunken Calf leather case, USB Type-C charging cable, quick start guide with documentation, and warranty information. Personally, I think that every DAP should come with a case, regardless of the hi-fi manufacturer. Unlike smartphones, there aren't 1,001 brands making knockoff cases for us to buy aftermarket for our DAPs. We get one case from the manufacturer that we should buy at the time of purchase if it's not already included. The SP4000's case is no different from other AK DAP cases, and the taupe, almost gray-toned color is beautiful and will definitely appeal to everyone.
Sound
As audiophiles, our goal is to achieve the most accurate sound reproduction of our favorite songs. A truly great component will enhance your listening experience without adding unnecessary coloration. Finding a DAP capable of achieving this task seems nearly impossible – that is, until the SP4000 DAP hit the market.
The A&ultima SP4000 DAP flexes its sonic muscle as a portable player capable of delivering an accurate, natural, and dynamic sound quality. Whether you own one pair of headphones, five, or an entire collection, the SP4000 will complement each one of them. Astell&Kern DAPs are prized for their detail retrieval, accuracy, and dynamic range–among other qualities–and the SP4000 is the perfect representation of AK's signature sound.
After a successful weekend at my first festival, Gov Ball in Queens, New York, I came back to work with a repertoire of new artists and songs to discover–Just in time for the SP4000's arrival at my desk. There's something so refreshing about finding new music, especially when you review products for a living. The most surprising artist for me at the festival was Raye, a British singer & songwriter, who, aside from her radio hits, I know little about. Diving into her most popular songs first with the Dan Clark Noire XO Headphones and Blue Dragon Premium Headphone Cable as my guide, I was immersed in a world of club-style techno beats with reverb vocals, synths, and everything in between. The SP4000 handled each change during these tracks like a skilled technician. Something akin to the lead member of a pit crew.
Glass Animals is another group I enjoyed live for the first time, and I was thrilled to hear they sounded as good, if not even better, live than they did digitally. Anyone who's been to enough concerts knows that not every artist sounds the same live. Having experienced that disappointment a few times before, it's a grim reality that I like to ignore. With the only IEMs fit for the job, the 64 Audio U12t IEMs (paired with the Silver Dragon IEM Cable) I selected my favorite Glass Animals song Creatures In Heaven and floated away to paradise.
The SP4000 transported me back to the pit of their show, where I was enamored by the emotion and passion of the lead singer's performance. Lyrics that once sounded jumbled up and incredibly fast over my car speakers were clear as day and incredibly musical. From the piano to the guitars and percussion, every instrument had its own space and presence. The U12t IEMs proved to be the perfect match for the SP4000. Vocals were rich and immersive, with well-articulated and extended highs. I found myself daydreaming out the window, forgetful of the fact that I needed to listen critically. A piece of gear that can take me out of reality and throw me into sonic bliss is something worth owning.
The SP4000 has the hallmarks of a flagship DAP: A Wide soundstage. Great dynamic range. Quick response and articulation. Nice detail retrieval, texture, and layering. It's immersive and harmonious while also maintaining instrument separation and space. Listening with IEMs was a breeze, and harder-to-drive over-ear headphones like the Dan Clark Audio NOIRE XO even fared well too.
Take everything you love about the SP3000, elevate it slightly, and you've got the SP4000.
MEDIA & ENTERTAINMENT
Confession: I'm a reality TV junkie. Yep, I love trashy TV and I'm not afraid to admit it. In between new episodes of my routine shows, I'm indulging in podcasts and talk shows centered around pop culture and reality recaps. YouTube is my go-to hub for this, so it felt fitting to check out the experience on the SP4000. Paired with the U12t IEMs, I pleasantly enjoyed a podcast episode of The Viall Files in breathtaking clarity.
Most podcast productions use high-quality microphones and headphones from brands like Shure and Sennheiser, and when I'm listening on my Apple AirPods or computer speakers, I don't pay much attention to the sound quality. Within the first five seconds of The Viall Files episode, I noticed improvements in the sound quality. The introductory song was more dynamic with a well-articulated low-end that's virtually undetectable in my usual listening setup. The hosts' voices sound clear and incredibly present as if I'm sitting in the same room as them. Not to mention the vibrance and clarity of the SP4000's touch screen were a significant upgrade to my Apple iPhone 13 Mini.
While on YouTube, I checked out some music videos and gameplay clips to get a good feel for the SP4000's sound quality and performance. No complaints, great experience all around.
Obsessed
By Olivia Rodrigo
(GUTS)
Black Mascara
By Raye
(My 21st Century Blues)
Criminals
By Meghan Trainor
(Timeless)
Creatures In Heaven
By Glass Animals
(I Love You So F***ing Much)
Features
- Enhanced signal processing capabilities with Octa audio circuit architecture
- Supports High Driving Mode for delivering premium sound quality
- Minimizes group delay with proprietary ESA (Enhanced Signal Alignment) technology
- Ultra Low Noise LDO Regulator for top-tier noise suppression
- Precision sound achieved with Any Layer Type PCB
- Equipped with a 99.9% Pure Copper Shield Can
- First Astell&Kern Device to Support Full Android OS
- First Astell&Kern Device to Feature Advanced DAR Technology
- Features 4.5th generation UI, combining functionality and emotional design
The Astell&Kern SP4000 DAP is full of new features and upgraded technology that make this player truly remarkable. With each new DAP release from AK, I find myself wondering, "What more could they possibly improve?" And as if they're reading my mind, they surprise me with something new.
Full Android OS with 4.5th Generation UI
The largest improvement over previous models is the full Android OS operating system, enabling bit-perfect lossless streaming through proprietary ADP (Astell&Kern Direct Path). AK DAPs have always run on the Android OS, but they've lacked some of the features that a full Android OS device supports. What features, you ask? The ability to install apps via the Google Play Store, for starters. This is a HUGE addition! Up to this point, app functionality was limited on AK DAPs. Allowing users to download their own apps unlocks a world of possibilities and an incentive for current AK DAP owners to upgrade.
While the SP4000 DAP supports full Android OS, it's still just a music player, so you won't have all of the settings and extended features you get from an Android OS smartphone. I imagine that's a given, but it's important to clarify in case anyone isn't familiar with AK DAPs or Android devices. Furthermore, some apps may experience compatibility errors due to Android system issues, so don't be surprised if the latest version of Fortnite isn't available. Just remember, it's not always the DAP's fault.
Now, downloading a thousand games and apps won't fare well for the DAP's performance and battery life. While you can download anything from HBO Max to Call of Duty Mobile, Candy Crush, and Twitch, you want to be mindful of the demand each app adds to the system–you don't want to overload it. As with anything, sometimes less is more.
The Google Play Store on the SP4000 is no different than it is on any other device. Once launched, you've got access to the store's entire suite of apps. You'll follow the same process you do on your devices, searching for apps by category or directly by name. From media streaming services to books, games, work apps, and more, the options are endless. Because the SP4000 is just a music player and doesn't have cellular data, apps requiring Wi-Fi (i.e., media and music streaming) won't have their full functionality, so download those TV shows and songs before heading out for the day.
Once logged into our Google account, we had no issues navigating the Google Play Store and downloading several apps. Managing your apps is done directly in the Google Play Store. This is where you'll find information on updates, and you can delete anything you're no longer using.
To support this new functionality, Astell&Kern has added a dedicated App Drawer, accessible on the SP4000's home screen. Simply click on the icon located at the bottom center of the home screen (just above the menu), and the drawer will open, showcasing your downloaded apps and the Google Play Store. You can rearrange the apps' order, but you cannot group them into sections like you can on the Apple iPhone. Much like a smartphone, though, you can view all of the apps currently open on the SP4000 and close them individually by swiping up or selecting the "close all" button. Click the far left icon (next to the home icon) on the bottom navigation bar to access this view. Routinely closing recently used apps is essential to maintaining the SP4000's impeccable performance.
One last addition to the user interface that's worth noting is the VU Meters. This is the third AK DAP to feature the meters, first appearing on the SP3000T and later SP3000M. The VU meter is conveniently accessible via the bottom navigation bar, so you can experience the duality of a vintage-inspired meter on a high-tech 21st-century product–LOL.
DAP, Circuit Design & Amplification
The SP4000 features several internal upgrades that make it worthy of its newly appointed flagship status. After several years of R&D, Astell&Kern has successfully implemented a True Quad DAC Architecture in the SP4000. While the SP3000 used a 1:2 digital-to-analog processing ratio, the SP4000 evolves to a precision 1:1 architecture. In this new structure, each AK4191 digital processor pairs with a dedicated AK4499EX DAC, delivering digital signals directly without noise distribution.
The SP4000 achieves its Octa Audio Circuit Architecture with four AK4499EX DAC chips and four AK4191 digital processors. The enhanced signal processing capabilities of the SP4000 enable it to achieve an impressive SNR of 131 dB (130 dB on SP3000).
The SP4000 takes it up a notch with twice as many OPAMPs arranged in a parallel configuration compared to previous models. High Driving Mode provides powerful and stable output to your headphones or IEMs so you can enjoy a deeper, clearer, and more immersive listening experience with nuance and fine details. By arranging the OPAMPs in a parallel configuration, the driving range expands horizontally with no increase in noise or reduction in the signal-to-noise ratio.
Series Configuration
Parallel Configuration
Flagship-Level CPU & Ultra-Low Noise Power Supply
The SP4000 features the same Snapdragon 6125 Octa-core processor and high-performance CPU with 8GB of DDR4 memory as the SP3000. The CPU, memory, and wireless communication parts are configured in one module, with the digital circuit parts arranged in the same area, creating a single system on a chip (SoC). This maximizes the efficiency of the overall circuit configuration by providing more audio-only circuit space as well as reducing heat and noise from digital circuits.
The SP4000 incorporates a newly implemented LDO (Low Dropout) Regulator that reduces noise by up to 97% compared to previous models. These high-performance components, typically reserved for precision medical devices and 5G communication equipment, stabilize battery voltage and effectively suppress noise for exceptionally clean, pure sound reproduction.
Additional Performance Enhancing Technology
The second generation of Digital Audio Remaster (DAR) technology is used in the SP4000, delivering a more natural, refined sound quality to your music. Rather than sending the audio file directly to the DAR engine, the SP4000 first uses VSE (Virtual Sound Extender) to virtually restore lost harmonics, enhancing the sound quality at the initial stage. Then, the advanced DAR engine performs a second-stage upsampling process with greater precision and completeness. This two-step approach allows listeners to enjoy a deeper, more immersive sound experience that comes closer than ever to the original recording.
[Lossy audio above 16kHz]
[Data restoration through VSE]
[DAR applied after data restoration]
ESA technology addresses the problem of group delay by aligning frequency signals to arrive more uniformly, minimizing frequency distortion, and dramatically enhancing sound clarity and purity. ESA technology ensures all frequencies arrive simultaneously for pristine, coherent sound quality. To achieve maximum sound quality, the SP4000 DAP features top-tier Any Layer HDI (High-Density Interconnect) PCB technology. This advanced circuit board design enables precise routing of complex circuitry within compact spaces while minimizing signal loss for refined, detailed sound delivery.
[Without ESA]
[With ESA]
For the first time in Astell&Kern's lineup, the SP4000 employs a precision-engineered Shield Can made from 99.9% pure copper. This advanced shielding blocks electromagnetic interference and various noise sources that could affect the audio block, delivering high-quality sound that is clearer and more distinct than ever before.
Listeners can alter the sound quality with the same six DAC filters featured in the SP3000 and enable crossfeed for that speaker-like effect when listening through headphones. AK File Drop, BT Sink, and ReplayGain are all still available.
Dragon Cables
[Silver Dragon Premium USB Cable]
There are a lot of reasons why you need to make sure your audio cables are not afterthoughts.
With the Silver Dragon Premium USB Cable, you can connect the SP4000 DAP to your computer or existing audio system and ensure your signal is transferred without degradation or noise interference. The Silver strands of the Silver Dragon Premium USB Cable enhance the detail, clarity, and resolution of the sound quality. When you're investing in a high-quality DAP, a high-quality cable just makes sense.
Verdict
So there you have it. At $3,900, the Astell&Kern A&ultima SP4000 DAP is the best thing since sliced bread. Is it worth upgrading? Short answer, yes. Long answer: The full Android operating system takes functionality to the next level, and if you're someone who uses multiple apps for music and entertainment, it's a no-brainer.
The SP4000's sound quality is about as reference as it gets for an AK DAP, so if audio nirvana is what you're searching for, you just might find it here. Look, life's short. Make the upgrade. Indulge in the sonic bliss and don't forget to upgrade your cable to a Silver Dragon Premium USB Cable. Why? Because every last percentage point counts when you're chasing sonic perfection.
For serious audiophiles who demand the absolute best in sound reproduction alongside modern functionality, the A&ultima SP4000 DAP delivers on every promise.
Featured Products
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Astell&Kern SP3000 DAP Music Player Review
Astell&Kern SP3000M DAP (Digital Audio Player) Review
Astell&Kern PD10 Review: This DAP Doubles as a Home Streamer
What's in the Box
- Astell&Kern A&ultima SP4000 Digital Audio Player
- Premium Perlinger Shrunken Calf leather case (German craftsmanship)
- USB Type-C charging cable
- Quick start guide and documentation
- Warranty information
Specifications
Model: SP4000 (PPF51)
Body Color: Black, Silver
Body Material: Stainless Steel 904L
Display: 6-inch 2K (2160 x 1080) touch screen
Wi-Fi: 802.11 a/b/g/n/ac (2.4/5GHz)
Bluetooth: V5.0 (A2DP, AVRCP, aptX™ HD, LDAC, LHDC, SBC, AAC)
Dimensions: 3.34” (85mm) [W] x 5.89” (149.8mm) [H] x 0.76” (19.5mm) [D]
Weight: Approx. 21.7oz (615g)
Feature Enhancements: Firmware upgrade supported (OTA)
Operating Temperature: 0℃ ~ +40℃ (32℉ ~ 104℉)
Supported OS: Windows 10/11 (32/64-bit), macOS X 10.7+
Storage Capacity: Built-in Memory 256GB NAND
External Memory: microSD x1 (Max 1.5TB)
CPU: Octa-core
DAC: AKM4191 x4 + AKM4499EX x4 (Real Quad DAC)
Clock Source: Clock Jitter: 25pS (Typ)
Reference Clock Jitter: 200 Femtoseconds
Battery:
Capacity: 6,780mAh 3.8V Li-Polymer
Charge Time: About 4 hours (QC3.0)
Playback Time: About 10 hours (FLAC, 16bit, 44.1kHz, Vol.50, LCD Off)
Additional Notes:
Audio measurements are based on Normal mode.
Auto Mute is not used during testing.
Supported Audio Formats: WAV, FLAC, WMA, MP3, OGG, APE, AAC, ALAC, AIFF, DFF, DSF
Sample Rate:
PCM: 8kHz ~ 768kHz (8/16/24/32 bits per Sample)
DSD Native: DSD64 (1bit 2.8MHz, Stereo), DSD128 (1bit 5.6MHz, Stereo),
DSD256 (1bit 11.2MHz, Stereo), DSD512 (1bit 22.4MHz, Stereo)
Output Level: Unbalanced 4.1Vrms │ Balanced 8.2Vrms (No Load)
Frequency Response:
±0.006dB (20Hz~20kHz) Unbalanced │ Balanced
±0.06dB (20Hz~70kHz) Unbalanced │ Balanced
S/N: 129dB @ 1kHz, Unbalanced │ 131dB @ 1kHz, Balanced
Crosstalk: -136dB @ 1kHz, Unbalanced │ -145dB @ 1kHz, Balanced
THD+N: 0.0005% @ 1kHz, Unbalanced │ 0.0003% @ 1kHz, Balanced
IMD SMPTE: 0.0004% (800Hz/10kHz 4:1), Unbalanced │ Balanced
Output Impedance: Unbalanced 3.5mm: 0.7Ω │ Balanced 4.4mm: 1.7Ω
Decoding Support: Up to 32-bit/768 kHz Bit-to-Bit Playback
Input: USB Type-C (for charging & PC/MAC)
Outputs:
Unbalanced Out (3.5mm), Optical Out (3.5mm),
Balanced Out (4.4mm, 5-pole only)
